1. Field of the Invention
This invention relates to a golf ball, more particularly, to a golf ball featuring a drastically improved degree of freedom of dimple design, improved flight performance, and symmetry. It also relates to a mold for use in the molding of such golf balls.
2. Prior Art
Golf balls are generally manufactured by using a mold including a pair of mold sections which are removably mated to define a spherical cavity therein and by feeding a stock material into the cavity. The parting line between the mold sections is a straight line rather than curvilinear for the purpose of simplifying mold manufacture. The linear parting line is coincident with the equator line on the golf ball surface. When a golf ball is molded in the mold, no dimples are formed on the equator line corresponding to the parting line and a great circle having a certain width is defined on the spherical surface.
For the golf ball having on the equator line a relatively wide great circle band which does not intersect with dimples, however, it is difficult to uniformly distribute dimples on the golf ball spherical surface. The ball is thus more or less non-uniform in aerodynamic symmetry. The flight performance varies with a particular position at which the ball is hit.
In order to overcome the above-mentioned problems, golf balls which eliminated a wide great circle band on the equator line and have dimples on the equator line were proposed in JP-A 173907/1986 and 143349/1994. These proposals are briefly described with reference to FIGS. 14 to 18. A mold is equally divided into two mold sections (only a lower mold section la is shown in FIG. 14), semi-circular grooves 2 are radially formed in the parting line or surface P of each mold section, and cylindrical members or pins 4 whose inner end defines a dimple-forming round protrusion 3 are fixedly received in the grooves 2. Using this mold, a golf ball having dimples lying across the equator line can be produced.
In this mold, however, the pins 4 are disposed such that their center 5 is aligned with the parting line P as shown in FIG. 15. As a result, the equator plane 8 passing the center 7 of the golf ball 6 obtained using this mold also passes the center of the dimple 9' lying astride the equator line as shown in FIGS. 16 to 18. Differently stated, the dimple 9' lying across the equator line 11 has the center coincident with the equator line 11 of the ball as best shown in FIG. 18.
Since the golf ball has dimples arranged such that some dimples are aligned with the equator line, the degree of freedom of dimple design is low due to such restriction while the spacing between the remaining dimples varies. This prohibits a diverse, high density, uniform dimple arrangement.
The golf ball molded using the above-mentioned mold wherein some dimples are aligned with the equator line has the likelihood that burrs form at the center of these dimples. Such burrs cannot be removed by conventional polishing techniques, but by the worker's manual operation, which results in low productivity. Further the finishing step includes surface polishing of the ball whereby an area adjacent the equator line is scraped off. Since the dimple edge is then lost, dimples with a sufficient depth are not available.